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BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



often as much as three inches in length. A specimen from 

 Benton presents interesting skeleton growths, which out- 

 line the half of an octahedron truncated by a cube. This 

 probably represents one phase of the Galena referred to 

 as reticulated galena in the report of the state geologist.' 

 The more beautiful feather-like skeleton growths have been 

 figured in that report. 



Fig. 5. — Aggregate of Galena from Mineral Point. 



At Mineral Point have been found large quite symmet- 

 rical cubes resembling those found at Highland. On some 

 specimens the faces of the galenas are studded with octa- 

 hedrons of pyrite which are superficially altered to limon- 

 nite. On the crystals of other specimens are found gray 

 cerussite crystals from 5-7 '"™ in diameter. Still another 

 series of specimens from Mineral Point presents very beau- 

 tiful aggregations of sub-individuals on which the octahe- 

 dron has a large development, forming hopper faced aggre- 

 gate individuals of the same habit (see figure 5). The 

 average size of the component individuals is only a few 

 millimeters and they are nearly perfect carbo-octahedrons, 

 but at the ends of each of the principal axes of the aggre- 

 gate crystal are large crystals with cubic habit, whose 

 cubic face determines the size of the cube face on the ag- 

 gregate crystal. The aggregate crystals have quite uni- 

 formly a diameter of about three to six centimeters and 



1 ChamberliD, Geol. of Wis., Vol. IV. p. 385. (1882.) 



